24 The Destructive Locust of the West. [ January, 
development of insect life. Now it is well known that in the 
Eastern States the summers of 1860 and 1874, preceding the ap- 
pearance of the army worm and grain aphis, were unusually 
warm and dry, and favorable not only for the hatching of the 
eggs laid the year previous, but for the growth and development 
of the larvæ or young. Look now at the conditions for the de- 
- velopment of locust life on the hot and dry plains, chiefly of Da- 
kota, Montana, Wyoming, and Idaho. We have no meteorolog- 
ical records from these regions at hand, but it is more than 
probable that the years preceding the migrations of the locusts 
were exceptionally warm and dry, when the soil was parched 
with long-sustained droughts, as we know that the corresponding 
species east of the Mississippi River abounds during dry sum- 
_mers following dry and warm springs. 
Given, then, the exceptional years of drought and heat and the 
great extent of territory, and we have as the result vast numbers 
of young hatched out. The year previous having perhaps been 
warm and dry, the locusts would abound, and more eggs than 
usual would be laid. These would with remarkably few excep- 
tions hatch, and the young soon consume the buffalo grass and 
other herbage, and move about from one region to another, fol- 
lowing often a determinate course in search of food. In this way 
large broods may migrate a long distance, from perhaps twenty 
to fifty miles. In about six or seven weeks they acquire wings. 
Experience shows that the western locust as soon as it is fledged 
rises up high in the air, sometimes a thousand feet or much 
higher. They have been seen to settle at night on the ground, 
eat during this time, and towards noon of the next day fill 
the air again with their glistening wings. As more and more 
become fledged, the vast swarm exhausts the supply of food, and 
when the hosts are finally marshaled, new swarms joining per- 
haps the original one, the whole swarm, possibly hundreds of 
miles in extent, begins to fly off, borne by the prevailing westerly . 
and northwesterly winds, in a general easterly and southeasterly 
course. 
(2.) The secondary cause of the migration is the desire for 
food, and possibly the reproductive instinct. The fact that in 
their migrations the locusts often seem to select cultivated tracts, 
rapidly cross the treeless, barren plains, and linger and die on the 
prairies and western edge of the fertile valleys of the Missouri 
and Mississippi, indicate that the impelling force is due primarily 
to the want of food, and that the guiding force is the direction 
